1. Field of the Invention
The present invention relates to a sensor-incorporated bearing assembly for wheels, having a built-in device that serves as a load sensor for detecting a load acting on a bearing portion of a wheel and/or an angle sensor for detecting the rotation angle of the wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the use has hitherto been made of a sensor on wheel support bearing assemblies for detecting the respective rotational speeds of wheels. In such a wheel support bearing assembly, it has been suggested in, for example, the Japanese Laid-open Patent Publications No. 2002-340922, published Nov. 27, 2002, and No. 2001-21577, published Jan. 26, 2001, to provide the bearing assembly with at least one extra sensor such as, for example, a temperature sensor, a vibration sensor or a load sensor so that in addition to the rotational speed, a parameter indicative of a condition useful in travel of an automotive vehicle can be detected.
While the measures for assuring the running safety of the automotive vehicle hitherto generally employed is practiced by detecting the rotational speed of each of vehicle wheels, it has however been found that the detection of only the rotational speed is insufficient and, therefore, it is increasingly desired that the control on the safety side can be accomplished with the use of any extra sensor signals. To meet this desire, it may be contemplated to control the vehicle attitude based on the load imposed on each of the vehicle wheels during the run of the automotive vehicle. By way of example, during cornering of the automotive vehicle, a larger load acts on outer vehicle wheels; during running on a transversely tilted surface, a larger load acts on vehicle wheels on one side of the automotive vehicle; and during braking, a large load acts on front vehicle wheels. Thus, the load does not always act on the vehicle wheels uniformly at all times during the run of the automotive vehicles.
Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. In view of this, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels, for example, can be controlled beforehand based on results of detection of the loads so that the attitude control of the automotive vehicle during the run thereof (for example, prevention of a rolling motion during the cornering, prevention of diving of the front wheels during the braking, and prevention of diving of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, no suitable space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Moreover, in the event that in the near future a steer-by-wire system, in which the wheel axle and the steering system are not coupled mechanically with each other, is introduced, transmission of information on the road surface to the steering wheel then held by a driver would be required by detecting a load acting in a direction parallel to the wheel axle.